A solid polymer electrolyte fuel cell is composed of one or more layers of cells, each of which is composed of a membrane-electrode assembly (MEA) and separators, stacked on top of each other. More specifically, the fuel cell stack is formed by disposing terminals (electrode plates), insulators, and end plates at both ends of a cell stack in the cell stacking direction, clamping the cell stack in the cell stacking direction and fixing it to fastener members (for example, tension plates) that extend outside the cell stack in the cell stacking direction with bolts.
In order to operate the fuel cell stack stably, a cell monitor for monitoring cell voltages is fixed, for example, above the fuel cell stack. In some cases, the cell monitor is, for example, as disclosed in Japanese Patent Laid-Open No. 2004-127779, attached to an outer surface of a fuel cell case with its cell monitor circuit board housed in a case with waterproof seal. In other cases, it may be fixed above the fuel cell stack via a case plate and be housed in the fuel cell case together with the fuel cell stack.